Recent studies have shown that the global mean sea level (GMSL) is accelerating. For improved process understanding and sea level projections, it is crucial to precisely estimate the GMSL acceleration due to externally-forced global climate change. For that purpose, the internal climate variability-related signal of the GMSL needs to be removed from the GMSL record. In the present study, we estimate how the observed GMSL rate has evolved with time over the altimetry era (1993-present), with the objective of determining how it is influenced by the interannual variability. We find that the GMSL rate computed over 5-year moving windows, displays significant interannual variability around 6–7 years and 12–13 years, preventing from robust acceleration estimation. To remove from the observed GMSL time series, the interannual variability, possibly related to internal climate modes, like ENSO, PDO, IOD, NAO or AMO, we use two methods previously widely applied in the literature: (1) multiple linear regression of the GMSL against some climate indices, and (2) Empirical Orthogonal Function (EOF) decomposition of the gridded sea level data to isolate the interannual signal. Although the interannual signal of the corrected GMSL time series is reduced, a cycle around 6–7 years still remains in the GMSL rate. We discuss possible sources of the remaining 6-7-year cycle, including the limitation of the methods used to remove the interannual variability.
Sea-level Rise, Coastal Flooding, and Storm Events
Sea level rise (SLR) is projected to have severe consequences for people and assets in European coastal areas. Planning for SLR is a critical step to ensure timely and adequate responses. Despite our rapidly increasing understanding of SLR impacts and the need to adapt, few studies have looked at how countries are planning for SLR. We surveyed experts from the 32 European countries with a coastline about how their country is planning for SLR. Our online survey focused on four areas: (1) whether SLR planning exists and at what level of government; (2) which climate information and scenarios are used in planning; (3) what planning horizons and corresponding levels of SLR are used; and (4) how uncertainty in handled and whether high-end sea level rise is being considered in planning. Additionally, we asked experts to assess the status of sea level rise planning in their country. Our results indicate that most coastal countries in Europe are planning for SLR, but 25% still do not. We find that the planning horizon 2100 is most common and many countries are considering around 1m (adjusted for local conditions) of SLR at that point in time. However, there are significant differences between countries, which may lead to unequal impacts, over time. We also find that RCP4.5 and RCP8.5 are the most widely used climate change scenarios, suggesting that countries are considering high-end climate change in planning, although this does not mean they consider high amounts of SLR. Important questions remain about how planning is realized into levels of protection or preparedness and whether the amounts of SLR and planning horizons currently in use will lead countries to act in time.
Ebb-tidal deltas filter incoming wave energy and mitigate erosion of basins and coasts by temporarily providing sediment. In many systems, these coastal safety functions are under threat from human activities. Here we use Delft3D/SWAN to assess the effects of relative sea-level rise and changes in basin area on the long-term dynamics of ebb-tidal deltas. The results show that the time scales of the cyclic channel-shoal dynamics of ebb-tidal deltas are affected. An instantaneous decrease in basin area slows down the cyclic behavior during the initial adjustment period. The duration of the adjustment period increases with larger basin area reduction. After the adjustment, smaller basins have shorter time scales of cyclic channel-shoal dynamics. This is linked to a decrease in tidal prism and ebb-tidal delta volume. Moreover, we find that the effects of relative sea-level rise depend on the rate of rising water levels. For relatively low rates, the period of the cycles eventually shortens, whereas higher rates can cause longer periods. The volume of ebb-tidal deltas appears to be unaffected by relative sea-level rise; but because the average water depth increases, more energetic waves reach the basin. By showing how ebb-tidal deltas adjust to relative sea-level rise and basin area reduction and by unraveling the underlying mechanisms, this study contributes to our understanding of the long-term evolution of tidal inlets.
Distally deposited tephra from explosive volcanic eruptions can be a powerful tool for precise dating and correlation of sedimentary archives and landforms. However, the morphostratigraphic and chronological potential of ocean-rafted pumice has been under-utilized considering its long observational history and widespread distribution on modern and palaeo-shorelines around the world. Here we analyze the geochemical composition and elevation data of 60 samples of ocean-rafted pumice collected since 1958 from raised beaches on Svalbard. Comparison of pumice data with postglacial relative sea-level history suggests eight distinct pumice rafting events throughout the North Atlantic during the Middle and Late Holocene. Analyzed ocean-rafted pumice exhibit consistent silicic composition characteristic of deposits from Iceland’s volcanic system, Katla. Eruption-triggered jökulhlaups are key drivers of the transport of pumice from the Katla caldera to beyond the coast of Iceland and into the surface currents of the North Atlantic Ocean. Thus, the correlation of distinct, high-concentration pumice horizons from Katla deposited along raised Middle Holocene beach ridges in Svalbard further advocates for the persistence of the Mýrdalsjökull ice cap through the Holocene thermal maximum.
A regional frequency analysis (RFA) of tide gauge (TG) data fit with a Generalized Pareto Distribution (GPD) is used to estimate contemporary extreme sea level (ESL) probabilities and the risk of a damaging flood along Pacific Basin coastlines. Methods to localize and spatially granulate the regional ESL (sub-annual to 500-year) probabilities and their uncertainties are presented to help planners of often-remote Pacific Basin communities assess (ocean) flood risk of various threshold severities under current and future sea levels. Downscaling methods include use of local TG observations of various record lengths (e.g., 1–19+ years), and if no in situ data exist, tide range information. Low-probability RFA ESLs localized at TG locations are higher than other recent assessments and generally more precise (narrower confidence intervals). This is due to increased rare-event sampling as measured by numerous TGs regionally. For example, the 100-year ESLs (1% annual chance event) are 0.15 m and 0.25 higher (median at-site difference) than a single-TG based analysis that is closely aligned to those supporting recent Intergovernmental Panel on Climate Change (IPCC) assessments and a third-generation global tide and surge model, respectively. Height thresholds for damaging flood levels along Pacific Basin coastlines are proposed. These floods vary between about 0.6–1.2 m or more above the average highest tide and are associated with warning levels of the U.S. National Oceanic and Atmospheric Administration (NOAA). The risk of a damaging flood assessed by the RFA ESL probabilities under contemporary sea levels have about a (median) 20–25-year return interval (4–5% annual chance) for TG locations along Pacific coastlines. Considering localized sea level rise projections of the IPCC associated with a global rise of about 0.5 m by 2100 under a reduced emissions scenario, damaging floods are projected to occur annually by 2055 and >10 times/year by 2100 at the majority of TG locations.
Shallow tropical bays in the Caribbean, like Orient Bay and Galion Bay in Saint Martin, are often sheltered by coral reefs. In the relatively calm environment behind the reefs, seagrass meadows grow. Together, these ecosystems provide valuable ecosystem services like coastal protection, biodiversity hotspots, nursery grounds for animals and enhancing tourism and fisheries. However, sea-level rise imperils these ecosystems and the services they provide because of changing hydrodynamic conditions, with potential effects on the interdependencies between these ecosystems. By means of a hydrodynamic model that accounts for the interaction with vegetation (Delft3D Flexible Mesh), the impact of sea-level rise (0.87 m in 2100) is investigated for three scenarios of future reef development (i.e. keep-up, give-up and catch-up). If coral reefs cannot keep up with sea-level rise, the wave height and flow velocity increase significantly within associated bays, with the wave height doubling locally in case of eroding reefs in our model simulations. Since the presence of seagrass strongly depends on the hydrodynamic conditions, the response of seagrass to the future hydrodynamic conditions is projected using a habitat suitability model that is based on a logistic regression. The spatial character of the bays determines the response of seagrass. In Orient Bay, which is deeper and partly exposed to higher waves, the seagrass will likely migrate from the deeper parts to shallow areas that become suitable for seagrass because of the surf zone moving landward. In contrast, the conditions for seagrass worsen in Galion Bay for the catch-up and give-up scenario; due to the shallowness of this bay, the seagrass cannot escape to more suitable areas, resulting in significant seagrass loss. It is shown that healthy coastal ecosystems are able to limit the change in hydrodynamic conditions due to sea-level rise. Therefore, preserving these ecosystems is key for ensuring the resilience of shallow tropical bays to sea-level rise and maintaining their ecosystem services.
An uplifted atoll of Minami-Daito Island, Japan.
Major ions and stable isotopes (δ2H and δ18O) of groundwater at fifteen observation wells, surface water at eight representative lakes and one seawater site were measured to unravel the dominant processes controlling the chemistry of water, its spatial distribution and to identify the salinization mechanism caused by long-term sea-level rise.
New hydrological insights for the region
Rainfall is the main source for groundwater and lake water. Evaporation affects both the ion concentration and the stable isotopes of the lake water. Geochemical modeling suggests that freshwater-seawater mixing is the main process increasing concentrations of Na+, Cl−, Mg2+, and SO42−, whereas dissolution of calcite and dolomite increases concentrations of Ca2+, Mg2+, and HCO3− in groundwater. Fresh groundwater and lake water (i.e., Cl− < 500 mg/L) are largely distributed along a SW-NE direction, but they have been reduced since the 1970s. Sea-level rise causes an increase in the salinity of lake water by flowing through fractures being connected from lakes to the northern coast, then spreading to other lakes through the artificial channels built in the years.
Over the past two decades, natural calamities like tsunamis and earthquakes occur more frequently, posing a serious threat to the human race. About 80% of these calamities have the “Ring of Fire” in the Pacific Ocean as its epicenter, causing extreme destructions due to the huge amount of energy and moving water bodies striking the adjoining land masses. Tsunamis cause heavy damage to human lives killing almost 430,000 lives since 1850, as it is almost impossible to flee from the mammoth waves. Huge waves collapse concrete buildings causing electrocution, explosion of gas plants, breakage of tanks and industries due to the floating debris that comes along with the killer waves. Following a tsunami, loss of infrastructures and economies is inevitable. This paper highlights the types of tsunamis and their potential effects on built structures and explains the association between tsunami related injuries and household level risk factors, including damages to built environment. Earlier studies have revealed that women, children and elderly citizens are at greater risk, and proximity to sea shores increase their risk of being affected. This finding, together with the risk of living in permanent structures in tsunami threatened areas should be an eye opener for the policy makers.
Coastal flood impact assessments are important tools for risk management and are performed by combining the hazard component with the vulnerability of exposed assets, to quantify consequences (or impacts) in terms of relative or absolute (e.g. financial) damage. The process generates uncertainties that should be taken into account for the correct representation of the consequences of floods. This study presents a coastal flood impact application at the spatial level of the Stavanger municipality (Norway), based on a multi-damage model approach able to represent impacts, and their overall uncertainty. Hazard modelling was performed using the LISFLOOD-FP code, taking into account historical extreme water level events (1988–2017) and relative sea level rise scenarios. Direct impacts were calculated in the form of relative and financial damage for different building categories, using flood damage curves. The results showed that the expected impacts are fewer than 50 flooded receptors and less than €1 million in damage in the current sea level scenario. The impacts could double by the end of the century, considering the most optimistic relative sea level scenario. The results were discussed considering the limitations of the approach for both hazard and impact modelling, that will be improved in future implementations. The outcome of this study may be useful for cost–benefit analyses of mitigation actions and local-scale plans for adaptation.
A large amount of tsunami debris from the Great East Japan Earthquake in 2011 was sunk on the seafloor and threatened the marine ecosystem and local communities' economy, especially in fisheries. However, few studies estimated spatial accumulations of tsunami benthic debris, comparing to their flows on the ocean surface. Here, a spatially varying coefficient model was used to estimate tsunami debris accumulation considering the spatial structure of the data off the Tohoku region. Our model revealed the number of vessels nearest the coast at the tsunami event had the highest positive impact, whereas the distance from the coast and kinetic energy influenced negatively. However, the effect of the proximity to the coast wasn't detected in the Sendai bay, indicating spatial dependency of these effects. Our model estimation provides the fundamental information of tsunami debris accumulation on the seafloor, supporting early reconstruction and risk reduction in marine ecosystems and local communities.